1. A reference to an upward fold of stratified rock in which the sides slope down and away from the crest; the oldest rocks are i the center, and the youngest rocks are on the outside.
2. Sloping downward from a common crest in opposite directions, as in an anticline
3. An arch-shaped fold in rock in which rock layers are upwardly convex.

The oldest rock layers form the core of the fold, and outward from the core progressively younger rocks occur.

Anticlines form many excellent hydrocarbon traps, particularly in folds with reservoir-quality rocks in their core and impermeable seals in the outer layers of the fold.

A syncline is the opposite type of fold, having downwardly convex layers with young rocks in the core.